Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly. The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, normally, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.
In the power supply system including the fuel cell stack of this type, for example, in order to handle change in the power demand, or in order to handle a plurality of loads, a plurality of fuel cell stacks may be used in combination.
In the power supply system disclosed in Japanese Laid-Open Patent Publication No. 2009-043520, a plurality of fuel cells and a control device are provided. The power generation amounts of the fuel cells are controlled based on a signal received by control means capable of transmitting and receiving data. The control device is capable of transmitting and receiving data to and from the control means of the fuel cells. The control device includes electrical power load detection means for detecting an electrical power load, power generation amount detection means for detecting a power generation amount of each of the fuel cells, power generation amount accumulation means for accumulating the power generation amount detected by the power generation amount detection means for a predetermined period of time in each of the fuel cells, accumulated power generation amount clearing means for clearing the accumulated power generation amount when the power generation amount accumulated by the power generation amount accumulation means exceeds a predetermined threshold, operating order determination means for determining an operating order among the fuel cells, power generation amount determination means for determining the power generation amount for each of the fuel cells based on the electrical power load detected by the electrical power load detection means and the operating order determined by the operating order determination means, and transmission means for transmitting data of the power generation amount determined by the power generation determination means to the control means related to the fuel cells. The operating order determination means places the higher priority in the operating order, on the fuel cell having the larger power generation amount accumulated by the power generation amount accumulation means.
According to the disclosure, depending on the change in the electrical power load for each of the electrical consumers, by performing power generation from the fuel cell having the highest operating order among the fuel cells, the electrical power can be supplemented between the fuel cells at the maximum rated output with the best power generation efficiency. Further, by changing the operating order periodically, the total power generation amount of the fuel cells is averaged to equalize the aging deterioration in the fuel cells, and equalize the time for carrying out the maintenance operation, replacement operation of the fuel cells or the like.
Further, Japanese Laid-Open Patent Publication No. 2007-059359 discloses a method of controlling operation of a solid oxide fuel cell system including a plurality of solid oxide fuel cell stacks operated in combination. In the method, by independently controlling the flow rate of the fuel, the flow rate of the air, and the amount of load of each of the solid oxide fuel cell stacks, the overall power generation efficiency in the system is maximized.